How to Read Clouds

Much of our weather lore comes from sailors, farmers and hunters people who were most concerned with changing weather patterns.

Many weather sayings actually have a kernel of truth to them, based on empiricism the wisdom accumulated as people gained experience, even before the reasons behind the facts were uncovered. A good example of this can be found in the Bible.

In Chapter 16:2-3 there is a commentary on the weather first spoken by Christ:

"When it is evening, ye say, It will be fair weather: for the sky is red. And in the morning, It will be foul weather today: for the sky is red and lowring."

From this biblical quote probably evolved the oft-quoted sailor's mnemonic:

And indeed, If you have ever seen a red sky at sunset (when you're looking to the west), there likely is a high pressure system with dry air that is stirring dust particles in the air and causing the sky to look reddish.

Red sky

Since weather associated with prevailing winds and jet streams usually move from west to east, the dry air is heading towards you.

In contrast, a red sky in the morning (toward the east, where the sun rises) means that the dry air has already moved past you, and what follows behind it (on its way towards you) is a low pressure system that carries moisture.

If you watch the sky carefully over a span of weeks and months, and keep a diary or log of what you have observed, you'll soon be able to make some pretty good short-term weather forecasts of your own with a certain degree of accuracy.

In particular, watching the development and movement of the clouds can give you some pretty good clues as to what you might expect weathe-rwise over the next 24 to 48 hours.

What are clouds?

Clouds are composed of large collections of water droplets and/or ice crystals that are small enough to float through the air. They're formed when warm air containing water vapor cools and the water vapor condenses into minute droplets that come together.

Clouds are white because sunlight shines through them. Because the light is scattered through clouds at the same frequency, it doesn't usually break into colors as is the case with the prismatic effect of a rainbow. If clouds get thick enough that they obscure sunlight, they'll appear gray and dark. Shadows from other clouds can also contribute to this darkening.

Because clouds move with the wind, you can usually tell which way the wind is blowing and how strong the wind might be by watching the clouds.

The wide variety of different weather that we experience is accompanied by a wide variety of different types of clouds. The World Meteorological Organization (WMO) the official United Nations' authoritative voice on weather, climate and water recognizes 10 basic cloud types: cirrus, cirrostratus, cirrocumulus, altocumulus, altostratus, stratocumulus, nimbostratus, stratus, cumulus, and cumulonimbus.

Let's break this group down into four basic categories high, middle, low and vertical and take a look at some images of each to see how to recognize them and learn what kind of weather they indicate. Continue reading in this cloud image gallery.

Joe Rao

Joe Rao is a television meteorologist in the Hudson Valley, appearing weeknights on News 12 Westchester. He has also been an assiduous amateur astronomer for over 45 years, with a particular interest in comets, meteor showers and eclipses. He has co-led two eclipse expeditions and has served as on-board meteorologist for three eclipse cruises. He is also a contributing editor for Sky & Telescope and writes a monthly astronomy column for Natural History magazine as well as supplying astronomical data to the Farmers' Almanac. Since 1986 he has served as an Associate and Guest Lecturer at New York's Hayden Planetarium. In 2009, the Northeast Region of the Astronomical League bestowed upon him the prestigious Walter Scott Houston Award for more than four decades of promoting astronomy to the general public.